FindBugs
Static analysis tool finding bugs in Java bytecode (succeeded by SpotBugs)
Fit
Framework for Integrated Test: acceptance tests written as HTML tables
FitNesse
Wiki-based acceptance testing framework
FLUCTUAT
Static analyzer for numerical precision in C and Ada programs
Flyspray
Lightweight web-based bug tracking system in PHP
FogBugz
Project management and bug tracking with evidence-based scheduling